The present invention relates to the field of mass storage devices. More particularly, this invention relates to a disc drive that includes a slider, which is designed to maintain the fly height of the slider even though portions of the slider thermally expand during operation of the disc drive.
One of the key components of any computer system is a place to store data. Computer systems have many different places where data can be stored. One common place for storing massive amounts of data in a computer system is on a disc. The basic parts of any disc storage system are a disc that is rotated, an actuator that moves a transducer to various locations on or over the disc, and electrical circuitry that is used to write and read data to and from the disc. A typical disc storage system includes a microprocessor that controls most of the operations of the system. The microprocessor utilizes circuitry to encode data so that it can be successfully retrieved from and written to a medium on the disc.
A typical transducer translates electrical signals into magnetic field signals that actually record the data. The transducer is usually housed within a small ceramic block called a slider. The slider is passed over the rotating disc in close proximity to the disc. The transducer is used to read data from the disc or write information representing data to the disc.
The discs within conventional disc drives usually spin at relatively high revolutions per minute (RPM). A typical rotational speed is 7200 RPM but some high-performance disc drives rotate as fast as 10,000 RPM.
Sliders are aerodynamically designed to fly on a cushion of air that is generated due to rotating the discs at such high speeds. The slider has an air-bearing surface (ABS) that includes rails and a cavity or depression between the rails. The air-bearing surface is that surface of the slider nearest to the disc as the disc drive is operating. Air is dragged between the rails and the disc surface causing an increase in pressure that tends to force the head away from the disc. Air is simultaneously rushing past the cavity or depression in the air-bearing surface which produces a lower than ambient pressure area at the cavity or depression. The low-pressure area near the cavity counteracts the higher pressure at the rails. These opposing forces equilibrate so the slider flies over the surface of the disc at a particular fly height. The fly height is the distance between the disc surface and the transducing head. This distance is the thickness of an air lubrication film. This film minimizes the friction and resulting wear that would occur if the transducing head and disc were in mechanical contact during disc rotation.
Information that is in the form of data is stored on the surface of the discs. The data is divided or grouped together on the discs in certain portions or tracks on the discs. In some disc drives the tracks are a multiplicity of concentric circular tracks. Disc drive systems are configured to read and write information that is stored on the discs in one or more of the tracks.
The transducers are in the form of read/write heads that are attached to the sliders. One transducer is typically located on each side of a storage disc. The transducers read and write information to/from the storage discs when the transducers are accurately positioned over one of the designated tracks on the surfaces of the storage discs. As the storage discs spin, the appropriate read/write head is accurately positioned above the target track where the read/write head is able to store data onto a track by writing information representative of data onto the one of the discs. Similarly, reading data on a storage disc is accomplished by positioning a read/write head above the proper track, and reading the stored material from one of the storage discs.
In order to write on (or read from) different tracks, the read/write head is moved radially across the tracks on the disc to a designated target track. Servo feedback information is used to accurately locate the transducer. The disc drive control system moves the actuator assembly to the appropriate position using the servo information. The servo information is also used to hold the transducer in a steady position during a read or write operation.
The best performance of the disc drive results when a slider is flown as closely to the surface of a disc as possible. During operation of a disc drive, the distance between the slider and the disc is very small. Currently fly heights are about 0.5 micro-inches. It is contemplated that smaller fly heights will be achieved in the future since this is one factor in achieving increased recording density.
The constant demand for increasing hard drive recording density has resulted in a drastic decrease in fly height over the years. Variation in the fly height is an increasing source of problems due to head/media intermittent contact, especially at less than 0.5 micro-inch fly height. Intermittent contact induces vibrations that are detrimental to the reading/writing quality at such low fly height and may also eventually result in a head crash that causes the loss of data.
The slider body is typically formed from a ceramic wafer. The transducers are built on the wafer using conventional semiconductor processing techniques. The transducers are then encapsulated in an overcoat such as alumina. The wafer is sliced to form rows of individual heads and subsequently lapped to an appropriate dimension and surface finish. The individual heads are then diced from the rows to form individual sliders.
The interface between the alumina and the substrate typically includes the closest point between the slider and the disc when the slider is passing over the surface of the disc in transducing relation. As a result, if there is any variation in the fly height, this closest point is a likely contact point between the slider and the disc.
One source of variation in the fly height results from the differences in thermal expansion between the ceramic substrate and the transducer during operation of the disc drive. Due to intrinsic properties, the ceramic substrate and the transducer expand at different rates as the slider heats up. The differences in expansion cause the transducer to move closer to the disc surface than the substrate that is near the transducer. This change in spacing can affect the fly height of the slider. The varying fly height can cause poor disc drive performance during reading and writing operations. In addition, if the fly height becomes too small, there is likely to be contact between the slider and the disc during operation of the disc drive.
Therefore, what is needed is a slider that is capable of operating at low fly heights. In addition, there is a need for design that compensates for the differences in thermal expansion between the different parts in a slider. The resulting slider would be less sensitive to temperature variations during operation of the disc drive such that the disc drive operates in a more consistent manner.
The present invention relates to a slider for a disc drive. The slider includes a substrate having a cavity and a filler within the cavity. The slider further includes a transducer that is positioned near the filler. The invention includes the slider as well as the slider in combination with the disc drive.
The present invention also relates to a method of fabricating a slider. The method includes providing a substrate and forming a cavity in the substrate. The cavity is filled with a filler and a transducer is formed on the slider such that the transducer is positioned near the filler.
The slider and method of the present invention both include, or form, a cavity within a substrate. The filler material within the cavity has similar thermomechanical properties as the material of the transducer and/or the material of a layer that encapsulates the transducer. The design facilitates controlling the relative thermal expansion between the transducer and substrate of the slider. A center rail that includes the transducer may be formed on the slider such that the center rail includes a portion of the filler and a portion of the layer that encapsulates the transducer.
Compensating for, or minimizing, the thermal expansion of the transducer and the ceramic substrate provides a more consistent fly height of the slider during operation of the disc drive. In addition, the design adjusts the air-bearing surface of the slider such that the transducer does not extend below the rest of the slider as the transducer expands. The result is more consistent read and write performance characteristics amongst the heads in a disc drive as well as a design that is less sensitive to the differences in thermal expansion that exist between the substrate and the transducer of the slider and therefore is more robust to changes in ambient temperature.